In a digital broadcasting system, all the processes are performed on the basis of digital signals, so that video quality becomes clear and audio signals are finely classified into a range of from a low pitch sound to a high pitch sound so as to implement a high audio quality. Therefore, the digital broadcasting system has been rapidly applied and spread through various media such as terrestrial waves, satellites, cable TVs, and the like.
With respect to a test of a DTV receiver for receiving the digital broadcast described above, functions and performance of the receiver are tested by using signals received from the broadcasting system. However, although the test operation is available in the test utilizing an actual broadcasting system, particular signals for performing a test of a particular function of the receiver or uniformly maintaining the performance of the receiver are not provided. Therefore, in general, developers and manufacturers of the DTV receiver configures a virtual broadcasting system in order to perform function test and performance assessment and performs the DTV test utilizing the system.
On the other hand, in an analog TV system, in order to perform the video quality assessment for the video, a test signal (VITS: vertical interval test signal) is inserted into a vertical interval reference (VIR) area of each frame of the source video and is transmitted. The test signal is displayed on a measurement device such as an oscilloscope or a display device such as a monitor at a reception stage, so that the video quality of the video is assessed.
However, as it is difficult to use the above-described method for the digital TV, various approaches of an objective video quality assessment method for the video have been proposed. Particularly, a broadcasting transmission device transmits a source video after an encoding process such as compression is performed on the source video, and a reception device decodes the received video signal and displays the recovered video signal on a screen.
FIG. 1 is a schematic block diagram illustrating a video quality assessment system for a digital video according to a method of the related art. As illustrated in FIG. 1, a broadcasting transmission device 100 encodes an original source video by using an encoder, and after that, allows a channel-up converter to modulate and up-convert the encoded source video into an RF level and outputs the source video through a digital transmission link 104. A DTV receiver, that is, a broadcasting reception device 110 which receives a video signal as an RF signal in a set top box decodes the received video signal by using a decoder and outputs the decoded video signal to a display device, a video quality measurement device 120, and a measurement device such as an oscilloscope. The video quality measurement device 120 receives a reference signal including characteristic information on a video of which characteristics are extracted from a non-encoded original source video signal or original source video from a broadcasting transmission device by using a different channel and compares the received reference signal to the received, decoded source video to assess video quality, that is, a quality of the video.
In the video quality assessment method of the related art, since data need to be transmitted by using separate channels, there is a problem in that it is difficult to perform video quality assessment in real time at the same time of broadcasting (in an in-service state). In addition, in the video quality assessment method of the related art, the video quality is assessed by comparing an original source video or a reference signal including characteristic information to a decoded source video. However, there are shortcomings in that such a video quality assessment method is very complicated and an expensive video quality assessment system is required.
On the other hand, since visually-determined video quality is subjective in nature and is influenced by many factors, it is not easy to accurately measure the video quality. Therefore, various test methods for the subjective video quality assessment have been proposed. However, because of complicatedness and costs of the subjective video quality measurement method, methods of automatically determining the video quality by using algorithms have drawn much attention. Among the objective video quality assessment methods, the most widely used method is a method using a peak-signal-to-noise ratio (PSNR) which is calculated based on a mean squared error (MSE). The PSNR is measured in a log scale and is determined by a ratio between a square of the maximum number of samples which can exist in an image and a mean squared error (MSE) between an original image and a damaged image. Therefore, a high MSE value denotes a high difference to the original video and is measured as a low PSNR, so that the video quality is determined to be low. However, because of various reasons, in some cases, there is a problem in that assessment using the PSNR does not necessarily relate to actual subjective video quality.
Because of the above-described various problems, it is not easy to objectively assess the video quality of the digital TV.